Final answer:
Schist is the most commonly occurring type of metamorphic rock, alongside gneiss.
Step-by-step explanation:
The most commonly occurring type of metamorphic rock, in addition to gneiss, is schist. Schist is a medium- to high-grade, foliated metamorphic rock characterized by its platy or layered structure. It forms from the metamorphism of various rock types, such as shale, sedimentary rocks, or other schists.